The present invention relates generally to a backup of information stored on a storage system and more particularly to server-free backup of information on a storage area network (SAN).
With the increasing complexity of applications and the use of enormous amounts of information, the traditional model of servers controlling their storage devices has evolved into a Storage Area Network (SAN) model where the back-end storage functions are decoupled from the front end server applications. The servers and storage systems are connected together via high speed fiber-optic networks, i.e., Fibre Channels, and communicate using a Fibre Channel Protocol (FCP). The Fibre Channel paths are determined by high speed Fibre Channel Switches.
One major problem with a SAN was that the servers were still responsible for backup of their data. Thus a server needed to read in its data from a storage device, such as a disk system, and write it to a backup device, such as a tape or DLT library. With the present use of multi-terabyte databases, the backup function seriously reduced performance of the servers.
One prior art method of having a server-free backup was to off load the control of the storage system backup to the Fibre Switches (see the white paper, “Deliver Server-Free Back-up,” April 2000, Pathlight Technology, Inc., Ithaca, N.Y.). FIG. 1 shows such a prior art system that uses a Fibre Channel Switch to perform the back-up after receiving a command from the host or server, FIG. 1 shows a server 110 coupled to its storage system, i.e., disk system 114, via a SAN having Fibre Channel Switch 112. A Tape Library 116 which is used for backup is also connected to Fibre Channel Switch 112 via a Fibre channel. The server 110 issues an Extended Copy (E-Copy) command 118 to a Fibre Channel Switch 112. The E-Copy is a SCSI Primary Command 2 or a vendor specific command, such as from Legato® Systems, Inc. of Mountain View Calif. (referred to herein as Legato®) that instructs the copying of data from one logical device to another logical device. A copy manager in the Fibre Channel Switch 112 upon receiving the E-copy command from the Server 110 performs the Data transfer 120 by copying data from Disk System 114 to Tape Library 116. The copying proceeds under control of the Fibre Channel Switch 112 without need of server 110 action. Thus the server 112 is free to perform other tasks.
However, the above method of using the Fibre Channel Switches to control the back-ups also has problems. The Fibre Channel Switch 112 sends a read command to the disk system to retrieve back-up data. In addition the server 110 may also send a read command to the Disk System 114 to retrieve data for use in a user application. From the view point of the disk system 114, the disk system may not be able to distinguish between a read from the server 110 and a read for backup from the Fibre Channel Switch 112, thus the Disk System 114 may process both read commands with equal priority. However, the Disk System 114 should process the server read command before the less critical back-up read command.
In addition having the Fibre Channel switch 112 responsible for the heterogeneous disk system backups on a SAN leads to a complicated switch. Also the installed switches must all be compatible and may be required to be from only one vendor. And when the software or hardware on a disk system is modified or upgraded, the backup function of the Fibre Channel switch 112 may need to be changed. Thus using the Fibre channel switch as a back-up controller increases the equipment cost/complexity and maintenance burden.
Thus there is a need for an improved backup technique which further decentralizes the back-up of a storage system on a SAN to, for example, the storage system itself.